The invention relates to a data transmission method and system, and in particular, to a data transmission method and system in a motor vehicle occupant protection system.
EP 0 507 581 A1 discloses a data transmission system in which multiplex nodes are connected to a common bus line. In order to update the system, the multiplex nodes can transmit specific protocol words which comprise a data segment specifying a multiplex node group, and a confirmation signal segment. During the confirmation signal segment, each addressed multiplex node which is associated with the selected group can emit a confirmation signal. If all of the addressed multiplex nodes reply with a confirmation signal, the protocol word is repeated twice, for example. If some of the addressed multiplex nodes have still not replied, the nodes which do not reply are excluded from the registration list which lists the active nodes. If, on the other hand, a node which has not been active until then should reply for the first time, the registration list is supplemented with this node which replies for the first time.
With such a configuration, the known transmission collision problem, in which two or more nodes try to transmit at essentially the same time, may occur. In order to solve this problem, a priority sequence for the transmission authorization has to be predefined in each node, the priority sequence blocking transmission access to nodes with lower priority for as long as nodes with higher priority are transmitting. Therefore, before each bus access each node checks whether a node with a higher priority is not already transmitting, which can lead to a certain delay in the transmission of signals. In addition, a change in the fixed priority sequence is also problematic because the change has to be registered selectively in the multiplex nodes. In addition, synchronization problems may occur if the aim is to synchronize the timing clock of the operation of the individual multiplex nodes. In such a case, additional synchronization is necessary.
In one embodiment of the invention, there is a method of data transmission, comprising: transmitting an interrogation signal in a polling mode from a superordinate control unit to function units via a data bus, and transmitting a confirmation signal by the function units which are functioning and do not have any information to send, and when a confirmation signal is not received from a function unit, the superordinate control unit outputs a command signal which addresses the function unit and selectively causes it to transmit data.
In one aspect of the invention, the interrogation signal is transmitted cyclically.
In another aspect of the invention, the function units comprise impact and/or vehicle occupant detection sensors of a motor vehicle occupant protection system.
In still another aspect of the invention, the function units comprise firing caps for firing vehicle occupant protection means of a motor vehicle occupant protection system.
In yet another aspect of the invention, the interrogation signal comprises first signal segment for transmitting a polling command and a second signal segment which adjoins the second signal segment and which includes a multiplicity of regular voltage pulses which alternate between high and low potential.
In another aspect of the invention, the function units transmit confirmation signals in the form of current pulses during low level phases of voltage pulses of the signal segment.
In yet another aspect of the invention, the command signal has the same structure as the interrogation signal, and an address signal segment is provided instead of the signal segment which predefines the polling mode.
In still another aspect of the invention, an addressed function unit transmits its information in the form of current pulses during low level phases of voltage pulses of the command signal which adjoin the address segment, and generate check bits which are transmitted to the superordinate control unit after the transmission of information during further low-level phases of the command signal.
In another embodiment of the invention, there is a superordinate control unit; and a plurality of function units which are connected to the control/unit via a common data bus, in which the superordinate control unit is configured to repeatedly transmit an interrogation signal to the function units via the data bus, the interrogation signal requesting the function units to acknowledge the confirmation signal, and when the confirmation signal of one of the plurality of function units is not received, the control unit outputs a command signal which addresses the function unit and which requests it to transmit an information signal to the control unit.
In another aspect of the invention, the function units have voltage regulators which are connected to the data bus on the input side and which generate the supply voltage for the respective function unit from the interrogation signals and command signals.
In still another embodiment of the invention, there is a superordinate control unit; and a plurality of function units which are connected to the control unit via a common data bus and in which an interrogation signal is transmitted in a polling mode from the superordinate control unit to the plurality of function units via the data bus, and a confirmation signal is transmitted by the function units which are functioning correctly and do not have any information to send, and when a confirmation signal is not received from one of the plurality of function units, the superordinate control unit outputs a command signal which addresses the function unit and selectively causes it to transmit data.